Relation Between Strength and Hardness of High-Entropy Alloys

High-entropy alloys (HEAs) are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such potentials,high-throughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently required.Revealing the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness testing.However,up to now the strength-hardness relation for HEAs is still a puzzle.In this work,the relations between tensile or compressive strength and Vickers hardness of vari-ous HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is achieved.Data for hundreds of different HEAs were extracted from stud-ies reported in the period from 2010 to 2020.The results suggested that the well-known three-time relation (i.e.,hardness equals to three times the magnitude of strength) works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early fracture.However,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic (BCC) HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic (FCC) HEAs.As for dual-phase or multi-phase HEAs,similar 3-time relations can be also found.The present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.     

Microstructure,Mechanical Properties,and Corrosion Behavior of MoNbFeCrV,MoNbFeCrTi, and MoNbFeVTi High-Entropy Alloys

The development of high-entropy alloys(HEAs) has stimulated an ever-increasing interest from both academia and industries.In this work, three novel MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi HEAs containing low thermal neutron absorption cross section elements were prepared by vacuum arc melting. The microstructure, mechanical properties, and corrosion behaviors were investigated. A dominant body-centered cubic(BCC) phase was present in all these three HEAs. In addition,an ordered Laves phase was found to be another major phase in both MoNbFeCrV and MoNbFeCrTi alloys, whereas an ordered BCC(B2) phase was observed in the MoNbFeVTi alloy. The phase formation in these three alloys was discussed. It is found that the formation of the secondary phase in these alloys is mainly ascribed to the large atomic size difference and electronegativity difference. All the three HEAs show high hardness, high yield strength but limited plasticity. Moreover, the MoNbFeCrV, MoNbFeCrTi and MoNbFeVTi alloys exhibit excellent corrosion resistance in both deaerated 1 mol/L NaCl and 0.5 mol/L H _2 SO _4 solutions at room temperature. However, further composition adjustment and/or thermomechanical processing is required to enhance the mechanical properties of the three alloys.     

Microstructure and mechanical properties of equimolar FeCoCrNi high entropy alloy prepared via powder extrusion

An equiatomic FeCoCrNi high alloy (HEA) with both high tensile strength and ductility was produced by a powder metallurgy (P/M) method. The P/M process includes a gas atomization and a hot extrusion of pre-alloyed HEA powder. Microstructures and mechanical properties were characterized using optical microscopy (OP), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and tensile tests. The results show that the P/M FeCoCrNi HEA has a single face centered cubic (fcc) structure and an equiaxed microstructure. No obvious porosity and brittle intermetallic phase was found. The as-extruded alloy exhibits a very high tensile strength of 712.5 MPa, and still maintains an elongation as high as 56%. The improvement of the tensile properties is caused by the solid solution strengthening, grain boundary strengthening and homogenous microstructure. Therefore, the powder hot extrusion can be considered as a promising way for preparing large-sized HEAs with high mechanical properties.     

Nb添加对FeCo基合金高温性能与时效态性能的影响

对Fe-49Co-2V和Fe-49Co-2V-0.3Nb两种合金室温与高温时的磁性能和力学性能进行了测试。结果发现:与室温磁性能相比,两种合金在高温下的饱和磁化强度Bs与矫顽力Hc均降低;与室温力学性能相比,两种合金在500℃时的高温抗拉强度都有所增加,其中Nb元素的添加使合金力学性能强化的效果十分明显。两种合金经500℃时效处理168 h后,Fe-49Co-2V-0.3Nb合金经过高温时效后依然能保证具有良好的力学性能,添加了Nb元素后有助于改善合金的高温时效稳定性。     

Effects of Nb additions on the microstructure and mechanical property of CoCrFeNi high-entropy alloys

A series of five-component CoCrFeNiNb_x high entropy alloys (HEAs) were synthesized to investigate alloying effects of the large atom Nb on the structure and tensile properties. Microstructures of these alloys were examined using scanning electron microscopy and the phase evolution was characterized and compared using the ΔH_mix–δ and ΔX criteria. It was found that the microstructure changes from the initial single face-centered cubic (FCC) to duplex FCC plus hexagonal close-packed (HCP) structure with additions of Nb. The current alloy system exhibits a hypoeutectic structure and the volume fraction of the Nb-enriched Laves phase with the HCP structure increases with increasing the Nb content, which is mainly responsible for the increment in the yield and fracture strength. Particularly, the Nb_0.155 alloy containing a 9.3% Nb-enriched Laves phase exhibits the most promising mechanical properties with the yield strength and plastic strain as high as 321 MPa and 21.3%, respectively. The ΔH_mix–δ criteria well describe the phase selection for the thermally treated alloys, while the physical parameter ΔX fails to predict the appearance of the Nb-enriched Laves phase in this alloy system.     

高铝锌合金的铸态组织和机械性能关系分析

本文通过对比分析新研制的高塑韧性高强度锌合金和ZA27合金的显微组织,观察和分析了试样断口处显微组织的变化,研究了锌合金机械性能和显微组织间的关系,探讨了新研制合金塑韧性好的组织原因。     

Strong and Ductile Non-equiatomic High-Entropy Alloys: Design,Processing, Microstructure,and Mechanical Properties

We present a brief overview on recent developments in the field of strong and ductile non-equiatomic high-entropy alloys (HEAs). The materials reviewed are mainly based on massive transition-metal solute solutions and exhibit a broad spectrum of microstructures and mechanical properties. Three relevant aspects of such non-equiatomic HEAs with excellent strength–ductility combination are addressed in detail, namely phase stability-guided design, controlled and inexpensive bulk metallurgical processing routes for appropriate microstructure and compositional homogeneity, and the resultant microstructure–property relations. In addition to the multiple principal substitutional elements used in these alloys, minor interstitial alloying elements are also considered. We show that various groups of strong and ductile HEAs can be obtained by shifting the alloy design strategy from single-phase equiatomic to dual- or multiphase non-equiatomic compositional configurations with carefully designed phase instability. This design direction provides ample possibilities for joint activation of a number of strengthening and toughening mechanisms. Some potential research efforts which can be conducted in the future are also proposed.     

Effects of Chromium on the Microstructures and Mechanical Properties of AlCoCrxFeNi2.1 Eutectic High Entropy Alloys

In the present study,a series of AlCoCrxFeNi2.1 (x=0,0.25,0.5,0.75,1.0) eutectic high entropy alloys (EHEAs) have been designed and prepared.And the effect of Cr content on the microstructures and mechanical properties of the AlCoCrxFeNi2.1 alloys was systematically investigated.The results indicate that the AlCoCrxFeNi2.1 (x ＞ 0) alloys exhibit almost complete lamellar eutectic microstructures with a mixture structure of FCC and B2 phases.And the AlCoFeNi2.1 alloy without Cr element exhibited a hypoeutectic microstructure with a primary B2 phase.In addition,the eutectic microstructures for AlCoCrxFeNi2.1 eutectic alloys do not change significantly.The room temperature compressive tests results show that with an increase in Cr content (from x =0 to x =1.0),the yield strength will first decrease,and thereafter increase.The trend is the opposite with the fracture strength and plastic strain.They show an increase trend at first,and then decrease.The AlCoCr0.5FeNi2.1 (Cr0.5) alloy shows the best comprehensive mechanical properties.The tensile yield strength,fracture strength,and elongation are 536.5 MPa,1062 MPa,and 13.8％,respectively.Furthermore,the Cr0.5 alloy also displays a high strength with a yield strength of 362 MPa at 700 ℃.In summary,by changing the Cr content,AlCoCrxFeNi2.1 eutectic high entropy alloys with excellent comprehensive mechanical properties were obtained and prepared.     

8090 Al-Li合金的性能

8090 Al-Li合金是美国目前应用相当成熟的高强型合金，广泛应用于航空航天工业。8090 Al-Li合金具有密度低、弹性模量高、低温力学性能好等特点，而且在一定的变形条件下，具有一定的超塑性，但存在塑性低、各向异性严重等缺点。通过调整合金成分及采用适当的热处理可提高塑、韧性及减轻各向异性。     

Co含量对FeCoPB非晶合金软磁性能和弯曲韧性的影响

采用熔体旋淬的方法制备了Fe Co含量达到87 at%Fe-Co-P-B系非晶合金薄带,研究了金属元素Co对Fe-Co-P-B系非晶合金的形成能力、软磁性能和弯曲韧性的影响规律。该合金系具有高的饱和磁化强度1.75～1.84 T,且热处理后薄带仍具有良好的弯曲韧性。添加Co元素后,提高了合金的居里温度,矫顽力升高。对薄带样品施加12 MPa的拉应力,合金的矫顽力由12.8 A/m降低到6.5 A/m。因此,通过成分和应力的调控可以避免Fe基非晶合金热处理引起的弛豫脆性问题,为获得具有优异软磁性能和良好弯曲韧性的Fe基非晶合金提供重要途径。     

Effects of Mn Content on Mechanical Properties of FeCoCrNiMn_x (0≤x≤0.3) High-Entropy Alloys: A First-Principles Study

Effects of Mn content on mechanical properties of FeCoCrNiMn_x(0 ≤x≤0.3) high-entropy alloys(HEAs) are investigated via first-prmciples calculations combining EMTO-CPA method.Related physical parameters,including lattice constant.elastic constants,elastic modulus,Pugh's ratio,anisotropy factors,Poisson's ratio,Cauchy pressure,Vickers hardness,yield strength,and energy factor,are calculated as a function of Mn content.The results show that the resistances to bulk,elastic,and shear deformation decrease with increasing Mn content.Pugh's ratio B/G indicates that the ductility of FeCoCrNiMn_x HEAs has a remarkable reduction between 22 and 24% of Mn content.Meanwhile,Cauchy pressure suggests that the atomic bonding transforms from metallic to directional characteristic from 22 to 24% of Mn content.Vickers hardness and yield strength of FeCoCrNiMn HEA are intrinsically larger than those of FeCoCrNi HEA.Dislocation nucleation easily occurs in FeCoCrNiMn HE A compared to FeCoCrNi HEA,and large dislocation width in FeCoCrNiMnO_2 HE A results in low stacking-fault energy,which easily induces twinning deformation.This work provides a valuable msieht for further theoretical and experimental study on the mechanical properties of FeCoCrNiMn_x(0≤x≤0.3) HEAs.     

Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials.A fabrication strategy to meet this requirement is therefore in high demand.Herein,bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700-1000℃,and their microstructures as well as mechanical and magnetic properties were investigated.The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al-and Ni-rich body-centered cubic(BCC) matrix and Fe-and Mn-rich face-centered cubic(FCC)precipitates both in the grain interior and along the grain boundaries.The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy.The FCC volume fraction could be increased by increasing the annealing temperature,thereby offering tunable properties.The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800℃.The alloy annealed at this temperature had an average BCC grain size of 12±3μm and FCC volume fraction of 41±4%.Correspondingly,the s aturation magnetization and coercivity reached 82.57 Am~2/kg and 433 A/m,respectively.The compressive yield strength and fracture strength were 1022 and 2539 MPa,respectively,and the plasticity was 33%.Owing to its adjustable microstructure and properties,the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.     

Effects of electro-negativity on the stability of topologically close-packed phase in high entropy alloys

Topologically close-packed (TCP) phases with complex structures are often observed in high entropy alloys (HEAs). Currently, these TCP phases are garnering significant interest from both theoretical and experimental perspectives due to the ductility deterioration of the high strength HEAs. Alternatively, there are instances when TCP phases can actually benefit the mechanical performances of alloys, such as the wear resistance. Therefore, the stability of TCP phases should be taken into consideration in the alloy design. In this paper, the relationship between the TCP phase stability and the physicochemical/thermodynamic properties of alloying components in HEAs was systematically studied. The stability of TCP phases was found to correlate well with the electro-negativity difference (ΔX) for most of the reported HEAs. The stability of TCP phases is well delineated by the electro-negativity difference (ΔX): i.e., TCP phases are stable at ΔX > 0.133 except for some HEAs that contain a significant amount of aluminum.     

FCC结构高熵合金的析出强化研究进展

高熵合金是近年来涌现出的一种新型合金,突破了以一种或者两种元素为主、少量添加元素为辅的传统合金设计理念。作为高熵合金体系一个重要分支—FCC结构的高熵合金,具有高损伤容限、良好的抗辐照能力、高耐磨、耐腐蚀性能等一系列优异的性能,可以作为理想的工程结构材料。然而,FCC结构高熵合金强度-塑性不匹配严重制约了其工程应用。研究表明,析出强化可以有效提高FCC结构高熵合金的强度,产生优异的强度-塑性匹配性能,各国学者相继开发出大量的高性能析出强化高熵合金体系。本文主要介绍了FCC结构高熵合金的析出强化研究,包括非共格析出相和共格析出相,着重介绍了研究现状以及强韧化的影响机制,并对未来高熵合金析出强化研究进行了展望。     

Prediction of structure and elastic properties of AlCrFeNiTi system high entropy alloys

The effect of alloy compositions on structure and elastic properties of single-phase AlCrFeNiTi and AlCrFeNiTiX (X = V, Mn, Co, Zn, Zr, Nb, Mo and La) high entropy alloys was investigated by calculating solid solution characteristics of alloys combining with the first principles method. The obtained formation enthalpy, cohesive energy and mechanical stability indicated AlCrFeNiTi and AlCrFeNiTiX (X = V, Mn, Co, Nb and Mo) HEAs adopt the body centered cubic structure instead of face centered cubic structure. There is a rather good agreement between theoretical structure predictions and the classic criteria of valence electron concentration VEC. A detailed investigation on electronic structure of AlCrFeNiTi and AlCrFeNiTiX alloys revealed the bonding behavior of alloys. In addition, the calculated results of polycrystalline elastic parameters confirmed the ductility of AlCrFeNiTiX alloys would weaken with increasing mixing enthalpy ΔH_mix (or decreasing atomic size difference δ), and the increase in ΔH_mix is predicted to decrease the elastic anisotropy. Furthermore, we predicted that the present high entropy alloys should be more elastically isotropic when the corresponding the mixing enthalpy ΔH_mix has a larger value.     

Effect of Nb Content on Microstructure and Mechanical Properties of Mo0.25V0.25Ti1.5Zr0.5Nbx High-Entropy Alloys

High-entropy alloys (HEAs) have significant application prospects as promising candidate materials for nuclear industry due to their excellent mechanical properties, corrosion resistance and irradiation resistance. In this work, the Mo_0.25V_0.25Ti_1.5Zr_0.5Nb_x(x=0, 0.25, 0.5, 0.75 and 1.0) HEAs were designed and fabricated. The alloys were prepared by vacuum arc melting, and all the ingots were annealed at 1200°C for 24 h. The microstructures, ...     

FeMnCoCr系亚稳高熵合金的研究进展

高熵合金是一种原子排列有序,化学无序的新型多主元合金.通过改变合金元素的种类和浓度,能够调控合金系统层错能及显微组织的相稳定性,进而诱发形变孪晶、马氏体相变等塑性变形机制,最终使合金获得突出的综合力学性能.这种高熵合金的设计理念称为"亚稳工程".亚稳高熵合金的显微组织、相结构及变形机制与合金体系的层错能密切相关.在Fe...     

热处理对挤压镁合金AZ91和ZK60组织与性能的影响

通过力学性能测定以及金相显微组织观察,对挤压态AZ91和ZK60镁合金的热处理工艺进行了研究。结果表明,AZ91合金固溶态与挤压态相比抗拉强度变化不大,但伸长率有较大幅度的提高;时效硬度峰值时的抗拉强度与固溶态相比有一定的提高,但伸长率有较大幅度的降低。ZK60合金固溶态与挤压态相比抗拉强度和伸长率均有相当程度地降低,且时效硬度峰值时的抗拉强度与同溶态相比有一定的提高,伸长率也有较大幅度的降低。AZ91合金固溶处理后晶粒尺寸与挤压态相比有所增大,但ZK60合金固溶处理后晶粒尺寸显著粗化。同时,两种合金固溶时效处理后伴有强化相粒子析出。     

New Fe-based soft magnetic amorphous alloys with high saturation magnetization and good corrosion resistance for dust core application

Fe-rich amorphous dust core alloys with minor-addition of Mo and/or Cr were synthesized because of the industrial request of mass production of high efficient low core loss Fe-based dust cores. It was found that the present Fe-(Cr, Mo)-P-B-Si-(C) amorphous alloy ribbons exhibit good soft magnetic properties of above 1.5 T for saturation magnetization, below 10 A/m for coercivity and rather good corrosion resistance in 3%NaCl aqueous solution. Besides, the amorphous alloy ribbons exhibit good bending ductility in as-spun and optimally annealed states. It is noticed that these characteristics are much superior to those for commercial Fe-Cr-Nb-P-B-Si soft magnetic dust core alloy (SENNTIX). In addition, the annealing treatment was noticed to cause the improvement of corrosion resistance without detriment to bending ductility. The new Fe-based soft magnetic alloys with good combined characteristics are expected to be used as the basic material as high-efficient soft magnetic dust cores in a high frequency range.     

高强度铸造铝铜合金微观组织对性能的影响

研究了微观组织对ZL205A系铸造铝铜合金热处理后强度和塑性的影响。结果表明:影响该合金强度和塑性性能的微观组织主要是晶粒尺寸、晶内、晶界沉淀相,弥散析出相和未固溶相。晶界处主要是θ相、N相、初生T相的混合组织,当呈针状或条状时恶化合金性能,当呈半连续的骨骼对合金性能影响较小。晶内细小弥散的二次T相是主要强化相,当T相聚集长大会降低强度。过剩相θ相,当呈大块分布时降低合金塑性,当呈细小均匀分布时对合金性能影响较小。